vaadin-framework/client/src/com/vaadin/client/ui/dd/VDragAndDropManager.java

/*
 * Copyright 2000-2014 Vaadin Ltd.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.vaadin.client.ui.dd;

import com.google.gwt.core.client.GWT;
import com.google.gwt.core.client.Scheduler;
import com.google.gwt.core.client.Scheduler.RepeatingCommand;
import com.google.gwt.dom.client.Element;
import com.google.gwt.dom.client.EventTarget;
import com.google.gwt.dom.client.NativeEvent;
import com.google.gwt.dom.client.Node;
import com.google.gwt.dom.client.Style;
import com.google.gwt.dom.client.Style.Unit;
import com.google.gwt.event.shared.HandlerRegistration;
import com.google.gwt.user.client.Command;
import com.google.gwt.user.client.Event;
import com.google.gwt.user.client.Event.NativePreviewEvent;
import com.google.gwt.user.client.Event.NativePreviewHandler;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.user.client.ui.Widget;
import com.vaadin.client.ApplicationConnection;
import com.vaadin.client.ComponentConnector;
import com.vaadin.client.MouseEventDetailsBuilder;
import com.vaadin.client.Profiler;
import com.vaadin.client.UIDL;
import com.vaadin.client.VConsole;
import com.vaadin.client.ValueMap;
import com.vaadin.client.WidgetUtil;
import com.vaadin.client.ui.VOverlay;
import com.vaadin.shared.ApplicationConstants;
import com.vaadin.shared.MouseEventDetails;
import com.vaadin.shared.ui.dd.DragEventType;

/**
 * Helper class to manage the state of drag and drop event on Vaadin client
 * side. Can be used to implement most of the drag and drop operation
 * automatically via cross-browser event preview method or just as a helper when
 * implementing own low level drag and drop operation (like with HTML5 api).
 * <p>
 * Singleton. Only one drag and drop operation can be active anyways. Use
 * {@link #get()} to get instance.
 * 
 * TODO cancel drag and drop if more than one touches !?
 */
public class VDragAndDropManager {

    public static final String ACTIVE_DRAG_SOURCE_STYLENAME = "v-active-drag-source";

    /**
     * Implementation if this interface is provided as a parameter to
     * DDEventHandleStrategy methods. The mediator instance allows to manage
     * DnD.
     * 
     * @since 7.4.4
     */
    public interface DDManagerMediator {
        /**
         * Returns DnD manager instance.
         */
        VDragAndDropManager getManager();

        /**
         * Returns current drag event.
         */
        VDragEvent getDragEvent();

        /**
         * Clean up server communication callback.
         */
        void clearServerCallback();
    }

    private final class DefaultDragAndDropEventHandler implements
            NativePreviewHandler {

        @Override
        public void onPreviewNativeEvent(NativePreviewEvent event) {
            if (getEventHandleStrategy().isDragInterrupted(event,
                    managerMediator)) {
                // end drag if ESC is hit
                interruptDrag();
                event.cancel();
                event.getNativeEvent().preventDefault();
                return;
            }

            int typeInt = event.getTypeInt();
            if (typeInt == Event.ONKEYDOWN) {
                getEventHandleStrategy().handleKeyDownEvent(event,
                        managerMediator);
                return;
            }

            NativeEvent nativeEvent = event.getNativeEvent();
            currentDrag.setCurrentGwtEvent(nativeEvent);

            String display = getEventHandleStrategy().updateDragImage(event,
                    managerMediator);

            Element targetElement = getEventHandleStrategy().getTargetElement(
                    event, managerMediator);

            try {
                if (handleDragImage(targetElement, event)) {
                    return;
                }
            } catch (RuntimeException e) {
                // ApplicationConnection.getConsole().log(
                // "ERROR during elementFromPoint hack.");
                throw e;
            } finally {
                getEventHandleStrategy().restoreDragImage(display,
                        managerMediator, event);
            }

            getEventHandleStrategy().handleEvent(targetElement, event,
                    managerMediator);
        }

        private boolean handleDragImage(Element target, NativePreviewEvent event) {
            if (!WidgetUtil.isTouchEvent(event.getNativeEvent())
                    && getDragElement() == null) {
                return false;
            } else if (target == null) {
                // ApplicationConnection.getConsole().log(
                // "Event on dragImage, ignored");
                event.cancel();
                event.getNativeEvent().stopPropagation();
                return true;
            } else if (getEventHandleStrategy().handleDragImageEvent(target,
                    event, managerMediator)) {
                return true;
            } else {
                // just update element over and let the actual
                // handling code do the thing
                // ApplicationConnection.getConsole().log(
                // "Target just modified on "
                // + event.getType());
                currentDrag.setElementOver(target);
                return false;
            }
        }
    }

    /*
     * #13381, #14796. The drag only actually starts when the mouse move or
     * touch move event is more than 3 pixel away.
     */
    public static final int MINIMUM_DISTANCE_TO_START_DRAG = 3;

    private static VDragAndDropManager instance;
    private HandlerRegistration handlerRegistration;
    private VDragEvent currentDrag;

    private DDManagerMediator managerMediator = new DDManagerMediator() {

        @Override
        public VDragAndDropManager getManager() {
            return VDragAndDropManager.this;
        }

        @Override
        public VDragEvent getDragEvent() {
            return currentDrag;
        }

        @Override
        public void clearServerCallback() {
            serverCallback = null;
        }
    };

    private DDEventHandleStrategy eventHandleStrategy;

    /**
     * If dragging is currently on a drophandler, this field has reference to it
     */
    private VDropHandler currentDropHandler;

    public VDropHandler getCurrentDropHandler() {
        return currentDropHandler;
    }

    /**
     * If drag and drop operation is not handled by {@link VDragAndDropManager}s
     * internal handler, this can be used to update current {@link VDropHandler}
     * .
     * 
     * @param currentDropHandler
     */
    public void setCurrentDropHandler(VDropHandler currentDropHandler) {
        this.currentDropHandler = currentDropHandler;
    }

    private VDragEventServerCallback serverCallback;

    private HandlerRegistration deferredStartRegistration;

    public static VDragAndDropManager get() {
        if (instance == null) {
            instance = GWT.create(VDragAndDropManager.class);
        }
        return instance;
    }

    /* Singleton */
    protected VDragAndDropManager() {
    }

    private final NativePreviewHandler defaultDragAndDropEventHandler = new DefaultDragAndDropEventHandler();

    /**
     * Flag to indicate if drag operation has really started or not. Null check
     * of currentDrag field is not enough as a lazy start may be pending.
     */
    private boolean isStarted;

    /**
     * This method is used to start Vaadin client side drag and drop operation.
     * Operation may be started by virtually any Widget.
     * <p>
     * Cancels possible existing drag. TODO figure out if this is always a bug
     * if one is active. Maybe a good and cheap lifesaver thought.
     * <p>
     * If possible, method automatically detects current {@link VDropHandler}
     * and fires {@link VDropHandler#dragEnter(VDragEvent)} event on it.
     * <p>
     * May also be used to control the drag and drop operation. If this option
     * is used, {@link VDropHandler} is searched on mouse events and appropriate
     * methods on it called automatically.
     * 
     * @param transferable
     * @param nativeEvent
     * @param handleDragEvents
     *            if true, {@link VDragAndDropManager} handles the drag and drop
     *            operation GWT event preview.
     * @return
     */
    public VDragEvent startDrag(VTransferable transferable,
            final NativeEvent startEvent, final boolean handleDragEvents) {
        interruptDrag();
        isStarted = false;

        currentDrag = new VDragEvent(transferable, startEvent);
        currentDrag.setCurrentGwtEvent(startEvent);

        final Command startDrag = new Command() {

            @Override
            public void execute() {
                isStarted = true;
                addActiveDragSourceStyleName();
                VDropHandler dh = null;
                if (startEvent != null) {
                    dh = findDragTarget(Element.as(currentDrag
                            .getCurrentGwtEvent().getEventTarget()));
                }
                if (dh != null) {
                    // drag has started on a DropHandler, kind of drag over
                    // happens
                    currentDropHandler = dh;
                    dh.dragEnter(currentDrag);
                }

                if (handleDragEvents) {
                    handlerRegistration = Event
                            .addNativePreviewHandler(defaultDragAndDropEventHandler);
                    if (dragElement != null
                            && dragElement.getParentElement() == null) {
                        attachDragElement();
                    }
                }
                // just capture something to prevent text selection in IE
                Event.setCapture(RootPanel.getBodyElement());
            }

            private void addActiveDragSourceStyleName() {
                ComponentConnector dragSource = currentDrag.getTransferable()
                        .getDragSource();
                dragSource.getWidget().addStyleName(
                        ACTIVE_DRAG_SOURCE_STYLENAME);
            }
        };

        final int eventType = Event.as(startEvent).getTypeInt();
        if (handleDragEvents
                && (eventType == Event.ONMOUSEDOWN || eventType == Event.ONTOUCHSTART)) {
            // only really start drag event on mousemove
            deferredStartRegistration = Event
                    .addNativePreviewHandler(new NativePreviewHandler() {

                        private int startX = WidgetUtil
                                .getTouchOrMouseClientX(currentDrag
                                        .getCurrentGwtEvent());
                        private int startY = WidgetUtil
                                .getTouchOrMouseClientY(currentDrag
                                        .getCurrentGwtEvent());

                        @Override
                        public void onPreviewNativeEvent(
                                NativePreviewEvent event) {
                            int typeInt = event.getTypeInt();
                            if (typeInt == -1
                                    && event.getNativeEvent().getType()
                                            .toLowerCase().contains("pointer")) {
                                /*
                                 * Ignore PointerEvents since IE10 and IE11 send
                                 * also MouseEvents for backwards compatibility.
                                 */
                                return;
                            }

                            switch (typeInt) {
                            case Event.ONMOUSEOVER:
                                if (dragElement == null) {
                                    break;
                                }
                                EventTarget currentEventTarget = event
                                        .getNativeEvent()
                                        .getCurrentEventTarget();
                                if (Node.is(currentEventTarget)
                                        && !dragElement.isOrHasChild(Node
                                                .as(currentEventTarget))) {
                                    // drag image appeared below, ignore
                                    break;
                                }
                            case Event.ONKEYDOWN:
                            case Event.ONKEYPRESS:
                            case Event.ONKEYUP:
                            case Event.ONBLUR:
                            case Event.ONFOCUS:
                                // don't cancel possible drag start
                                break;
                            case Event.ONMOUSEOUT:

                                if (dragElement == null) {
                                    break;
                                }
                                EventTarget relatedEventTarget = event
                                        .getNativeEvent()
                                        .getRelatedEventTarget();
                                if (Node.is(relatedEventTarget)
                                        && !dragElement.isOrHasChild(Node
                                                .as(relatedEventTarget))) {
                                    // drag image appeared below, ignore
                                    break;
                                }
                            case Event.ONMOUSEMOVE:
                            case Event.ONTOUCHMOVE:
                                int currentX = WidgetUtil
                                        .getTouchOrMouseClientX(event
                                                .getNativeEvent());
                                int currentY = WidgetUtil
                                        .getTouchOrMouseClientY(event
                                                .getNativeEvent());
                                if (Math.abs(startX - currentX) > MINIMUM_DISTANCE_TO_START_DRAG
                                        || Math.abs(startY - currentY) > MINIMUM_DISTANCE_TO_START_DRAG) {
                                    ensureDeferredRegistrationCleanup();
                                    currentDrag.setCurrentGwtEvent(event
                                            .getNativeEvent());
                                    startDrag.execute();
                                }
                                break;
                            default:
                                ensureDeferredRegistrationCleanup();
                                currentDrag = null;
                                clearDragElement();
                                break;
                            }
                        }

                    });

        } else {
            startDrag.execute();
        }

        return currentDrag;
    }

    protected void updateDragImagePosition(NativeEvent gwtEvent,
            Element dragImage) {
        if (gwtEvent != null && dragImage != null) {
            Style style = dragImage.getStyle();
            int clientY = WidgetUtil.getTouchOrMouseClientY(gwtEvent);
            int clientX = WidgetUtil.getTouchOrMouseClientX(gwtEvent);
            style.setTop(clientY, Unit.PX);
            style.setLeft(clientX, Unit.PX);
        }
    }

    /**
     * First seeks the widget from this element, then iterates widgets until one
     * implement HasDropHandler. Returns DropHandler from that.
     * 
     * @param element
     * @return
     */
    protected VDropHandler findDragTarget(Element element) {
        try {
            Widget w = WidgetUtil.findWidget(element, null);
            if (w == null) {
                return null;
            }
            while (!(w instanceof VHasDropHandler)
                    || !isDropEnabled((VHasDropHandler) w)) {
                w = w.getParent();
                if (w == null) {
                    break;
                }
            }
            if (w == null) {
                return null;
            } else {
                VDropHandler dh = ((VHasDropHandler) w).getDropHandler();
                return dh;
            }

        } catch (Exception e) {
            // ApplicationConnection.getConsole().log(
            // "FIXME: Exception when detecting drop handler");
            // e.printStackTrace();
            return null;
        }

    }

    /**
     * Checks if the given {@link VHasDropHandler} really is able to accept
     * drops.
     */
    private static boolean isDropEnabled(VHasDropHandler target) {
        VDropHandler dh = target.getDropHandler();
        return dh != null && dh.getConnector().isEnabled();
    }

    /**
     * Drag is ended (drop happened) on current drop handler. Calls drop method
     * on current drop handler and does appropriate cleanup.
     */
    public void endDrag() {
        endDrag(true);
    }

    /**
     * The drag and drop operation is ended, but drop did not happen. If
     * operation is currently on a drop handler, its dragLeave method is called
     * and appropriate cleanup happens.
     */
    public void interruptDrag() {
        endDrag(false);
    }

    private void endDrag(boolean doDrop) {

        ensureDeferredRegistrationCleanup();
        ensureHandlerRegistrationCleanup();

        boolean sendTransferableToServer = false;
        if (currentDropHandler != null) {
            if (doDrop) {
                // we have dropped on a drop target
                sendTransferableToServer = currentDropHandler.drop(currentDrag);
                if (sendTransferableToServer) {
                    doRequest(DragEventType.DROP);
                    /*
                     * Clean active source class name deferred until response is
                     * handled. E.g. hidden on start, removed in drophandler ->
                     * would flicker in case removed eagerly.
                     */
                    final ComponentConnector dragSource = currentDrag
                            .getTransferable().getDragSource();
                    final ApplicationConnection client = currentDropHandler
                            .getApplicationConnection();
                    Scheduler.get().scheduleFixedDelay(new RepeatingCommand() {
                        @Override
                        public boolean execute() {
                            if (!client.getServerCommunicationHandler()
                                    .hasActiveRequest()) {
                                removeActiveDragSourceStyleName(dragSource);
                                return false;
                            }
                            return true;
                        }

                    }, 30);

                }
            } else {
                currentDropHandler.dragLeave(currentDrag);
                currentDrag.setCurrentGwtEvent(null);
            }
            currentDropHandler = null;
            serverCallback = null;
            visitId = 0; // reset to ignore ongoing server check
        }

        /*
         * Remove class name indicating drag source when server visit is done
         * iff server visit was not initiated. Otherwise it will be removed once
         * the server visit is done.
         */
        if (!sendTransferableToServer && currentDrag != null) {
            removeActiveDragSourceStyleName(currentDrag.getTransferable()
                    .getDragSource());
        }

        currentDrag = null;

        clearDragElement();

        // release the capture (set to prevent text selection in IE)
        Event.releaseCapture(RootPanel.getBodyElement());

    }

    private void ensureHandlerRegistrationCleanup() {
        if (handlerRegistration != null) {
            handlerRegistration.removeHandler();
            handlerRegistration = null;
        }
    }

    private void ensureDeferredRegistrationCleanup() {
        if (deferredStartRegistration != null) {
            deferredStartRegistration.removeHandler();
            deferredStartRegistration = null;
        }
    }

    private void removeActiveDragSourceStyleName(ComponentConnector dragSource) {
        dragSource.getWidget().removeStyleName(ACTIVE_DRAG_SOURCE_STYLENAME);
    }

    private void clearDragElement() {
        if (dragElement != null) {
            if (dragElement.getParentElement() != null) {
                dragElement.removeFromParent();
            }
            dragElement = null;
        }
    }

    private int visitId = 0;
    private Element dragElement;

    /**
     * Visits server during drag and drop procedure. Transferable and event type
     * is given to server side counterpart of DropHandler.
     * 
     * If another server visit is started before the current is received, the
     * current is just dropped. TODO consider if callback should have
     * interrupted() method for cleanup.
     * 
     * @param acceptCallback
     */
    public void visitServer(VDragEventServerCallback acceptCallback) {
        doRequest(DragEventType.ENTER);
        serverCallback = acceptCallback;
    }

    private void doRequest(DragEventType drop) {
        if (currentDropHandler == null) {
            return;
        }
        ComponentConnector paintable = currentDropHandler.getConnector();
        ApplicationConnection client = currentDropHandler
                .getApplicationConnection();
        /*
         * For drag events we are using special id that are routed to
         * "drag service" which then again finds the corresponding DropHandler
         * on server side.
         * 
         * TODO add rest of the data in Transferable
         * 
         * TODO implement partial updates to Transferable (currently the whole
         * Transferable is sent on each request)
         */
        visitId++;
        client.updateVariable(ApplicationConstants.DRAG_AND_DROP_CONNECTOR_ID,
                "visitId", visitId, false);
        client.updateVariable(ApplicationConstants.DRAG_AND_DROP_CONNECTOR_ID,
                "eventId", currentDrag.getEventId(), false);
        client.updateVariable(ApplicationConstants.DRAG_AND_DROP_CONNECTOR_ID,
                "dhowner", paintable, false);

        VTransferable transferable = currentDrag.getTransferable();

        client.updateVariable(ApplicationConstants.DRAG_AND_DROP_CONNECTOR_ID,
                "component", transferable.getDragSource(), false);

        client.updateVariable(ApplicationConstants.DRAG_AND_DROP_CONNECTOR_ID,
                "type", drop.ordinal(), false);

        if (currentDrag.getCurrentGwtEvent() != null) {
            try {
                MouseEventDetails mouseEventDetails = MouseEventDetailsBuilder
                        .buildMouseEventDetails(currentDrag
                                .getCurrentGwtEvent());
                currentDrag.getDropDetails().put("mouseEvent",
                        mouseEventDetails.serialize());
            } catch (Exception e) {
                // NOP, (at least oophm on Safari) can't serialize html dd event
                // to mouseevent
            }
        } else {
            currentDrag.getDropDetails().put("mouseEvent", null);
        }
        client.updateVariable(ApplicationConstants.DRAG_AND_DROP_CONNECTOR_ID,
                "evt", currentDrag.getDropDetails(), false);

        client.updateVariable(ApplicationConstants.DRAG_AND_DROP_CONNECTOR_ID,
                "tra", transferable.getVariableMap(), true);

    }

    public void handleServerResponse(ValueMap valueMap) {
        if (serverCallback == null) {
            return;
        }
        Profiler.enter("VDragAndDropManager.handleServerResponse");

        UIDL uidl = (UIDL) valueMap.cast();
        int visitId = uidl.getIntAttribute("visitId");

        if (this.visitId == visitId) {
            serverCallback.handleResponse(uidl.getBooleanAttribute("accepted"),
                    uidl);
            serverCallback = null;
        }
        runDeferredCommands();

        Profiler.leave("VDragAndDropManager.handleServerResponse");
    }

    /**
     * Returns DnD strategy to handle native preview events used by the manager.
     * 
     * Subclasses can override this method to return custom strategy or use GWT
     * deferred binding.
     * 
     * @return internal DnD native preview event handler
     */
    protected DDEventHandleStrategy getEventHandleStrategy() {
        if (eventHandleStrategy == null) {
            eventHandleStrategy = GWT.create(DDEventHandleStrategy.class);
        }
        return eventHandleStrategy;
    }

    private void runDeferredCommands() {
        if (deferredCommand != null) {
            Command command = deferredCommand;
            deferredCommand = null;
            command.execute();
            if (!isBusy()) {
                runDeferredCommands();
            }
        }
    }

    void setDragElement(Element node) {
        if (currentDrag != null) {
            if (dragElement != null && dragElement != node) {
                clearDragElement();
            } else if (node == dragElement) {
                return;
            }

            dragElement = node;
            dragElement.addClassName("v-drag-element");
            updateDragImagePosition(currentDrag.getCurrentGwtEvent(),
                    dragElement);

            if (isStarted) {
                attachDragElement();
            }
        }
    }

    Element getDragElement() {
        return dragElement;
    }

    private void attachDragElement() {
        if (dragElement != null && dragElement.getParentElement() == null) {
            ApplicationConnection connection = getCurrentDragApplicationConnection();
            Element dragImageParent;
            if (connection == null) {
                VConsole.error("Could not determine ApplicationConnection for current drag operation. The drag image will likely look broken");
                dragImageParent = RootPanel.getBodyElement();
            } else {
                dragImageParent = VOverlay.getOverlayContainer(connection);
            }
            dragImageParent.appendChild(dragElement);
        }

    }

    private Command deferredCommand;

    private boolean isBusy() {
        return serverCallback != null;
    }

    protected ApplicationConnection getCurrentDragApplicationConnection() {
        if (currentDrag == null) {
            return null;
        }

        final ComponentConnector dragSource = currentDrag.getTransferable()
                .getDragSource();
        if (dragSource == null) {
            return null;
        }
        return dragSource.getConnection();
    }

    /**
     * Method to que tasks until all dd related server visits are done
     * 
     * @param command
     */
    private void defer(Command command) {
        deferredCommand = command;
    }

    /**
     * Method to execute commands when all existing dd related tasks are
     * completed (some may require server visit).
     * <p>
     * Using this method may be handy if criterion that uses lazy initialization
     * are used. Check
     * <p>
     * TODO Optimization: consider if we actually only need to keep the last
     * command in queue here.
     * 
     * @param command
     */
    public void executeWhenReady(Command command) {
        if (isBusy()) {
            defer(command);
        } else {
            command.execute();
        }
    }

}